3d printed spacers for ion-exchange device

ABSTRACT

The present disclosure is directed ion-exchange systems and devices that include composite ion-exchange membranes having 3D printed spacers on them. These 3D printed spacers can drastically reduce the total intermembrane spacing within the system/device while maintaining a reliable sealing surface around the exterior border of the membrane. By adding the spacers directly to the membrane using additive manufacturing, the amount of material used can be reduced without adversely impacting the manufacturability of the composite membrane as well as allow for complex spacer geometries that can reduce the restrictions to flow resulting in less pressure drop associated with the flow in the active area of the membranes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/449,951, filed Jun. 24, 2019, which claims the benefit of U.S.Provisional Application No. 62/689,357, filed Jun. 25, 2018, the entirecontents of each of which are incorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to membrane spacers for an ion-exchange device.More specifically, this disclosure relates to 3D printed spacers for usein an ion-exchange water treatment system.

BACKGROUND OF THE DISCLOSURE

The earliest forms of large scale desalination were thermal methods suchas thermal distillation where the water is boiled and converted intosteam, leaving behind the impurities, and then the clean steam iscollected and condensed. Unfortunately, this is a very energy intensiveoperation. In order to reduce the energy consumption, membrane basedmethods were created such as electro-chemical based electrodialysis andpressure driven reverse osmosis. In both of these methods, the water ispurified through a membrane which allows the system to create potablewater at a much reduced energy consumption.

Electrodialysis can be used to selectively remove positive and negativeions from a water source (e.g., brackish water or the brine solutionproduced in reverse osmosis units) through transportation of salt ionsfrom one solution to another via ion-exchange membranes upon applicationan electrical current. An electrodialysis device can include a pair ofelectrodes (where a voltage is applied to initiate an electrochemicalreaction), alternating anionic and cationic exchange membranes (whichcan selectively separate ions from one stream while concentrating saidions in adjacent streams from a dilute solution feed stream to aconcentrate stream), and spacer materials. These spacers can be placedbetween the ion exchange membranes. The primary function of thesespacers is to create turbulence in the flow field and to restrict themembranes from contacting one another.

Unfortunately, the electrical energy required to transport ions from onestream to another is a function of the resistance of the system viaOhm's law (V=i*R), where V is the electrical potential, i is the currentdensity, and R is the resistance. The resistance of the system can beimpacted by both the conductivity of the water in the unit (K) (whichconsequently decreases as the ions are removed), and the spacerthickness (L). Specifically, the resistance scales linearly with theintermembrane spacing as seen by the following equation: R=K⁻¹*L.

In a typical electro-chemical desalination device, the two electrodescan sandwich upwards of 1000 pairs of membranes and spacers. Thus, thesecomponents and the water filling them can make up a significant portionof the resistance in the device.

BRIEF SUMMARY OF THE DISCLOSURE

Applicants have discovered spacers and methods for preparing thesespacers that can reduce the resistance of the spacers between themembranes. Specifically, Applicants have discovered how to minimize thespacing between the alternating cationic and anionic exchange membranesin an electrodialysis-like device. Minimizing the spacer spacing canreduce the resistance in the device, thereby reducing the energyconsumption.

Typical spacers are on the order of 500-600 microns thick. Making aspacer thinner than this can be problematic for at least two reasons:(1) the pressure drop through the active area (area that is directlybetween the electrodes through which an electrical current may bepassed) can become too high; and (2) the material that the spacer ismade out of can be difficult to handle when it is thinner leading tomanufacturability issues. Furthermore, as the spacer becomes thinner, itcan become a less reliable sealing surface.

The pressure drop is a function of the height of the flow channel, andthus going to a thinner spacing can make the pressure drop greater. Ontop of this, adding a spacer in the flow field can act as an obstructionto the flow. Thus, Applicants discovered a spacer for a given flowchannel height, which can serve both to reliably separate the membraneand to still allow adequate flow. As an example in this space, wovenmaterials are often chosen as a spacer material. However, as the wirediameters become smaller, the weave necessarily must become tighter.Therefore, a weave with a nominal height of 500 microns could have anopen area of >65%, while a weave with a nominal height of 250 micronswould only have an open area of ˜50%. In addition, handling ability canbecome a critical issue to manufacturability. As the material becomesthinner, it can become less durable, more likely to crease, snag, andtear. Considering a stack of 1000 membrane pairs would have 2000spacers, these issues are magnified.

Furthermore, typical EDR stacks can utilize an elastomeric material forthe spacer border in which the elastomeric properties provide a goodseal but can degrade the consistency of flow channel thicknesses. Thisis due to the fact that elastomerics are compressible, so they sealwell, but have greater thickness and flatness variances, magnified bythe fact that there are upwards of 1000 pairs of these all incompression. In contrast, Applicants, in some embodiments, used a rigidand very flat PET spacer border for the sealing surface which canprovide good stackup tolerances and consistent flow channel thicknesses.In order for them to seal well, Applicants can apply 500 to 1500 psi ofpressure using our compression plates and utilize the membranes slightcompressibility to mitigate stackup tolerance issues.

Applicants have discovered advanced manufacturing techniques, such asadditive manufacturing (i.e., 3D printing) to make composite ionexchange membrane and spacers, wherein the total intermembrane spacingcan be reduced drastically (e.g., about 10-250 microns) whilemaintaining a reliable sealing surface around the exterior border. Thistechnique can solve the previously mentioned problems by first reducingthe amount of material necessary to serve as intermembrane spacers.Minimizing the amount of material used in the intermembrane spacers canreduce the restrictions to flow resulting in less pressure dropassociated with the flow in the active area and increase the membraneactive area resulting in more efficient ion transfer.

A conventional spacer requires additional material to provide rigidityduring installation. In contrast, by adding the spacers directly to themembrane using automated additive manufacturing devices, the amount ofmaterial used can be reduced without adversely impacting themanufacturability of the composite membrane (i.e., membrane plusspacers). In fact, handling of these composite membranes can be easierbecause the number of components that needs to be stacked can bereduced.

In addition to improved manufacturability, additive manufacturingtechniques can allow for the creation of shapes, features, and patternsof spacers that other processes and conventional spacers do not readilyallow. These shapes, features, and patterns formed with 3D printingtechniques can be engineered to improve hydrodynamics and respond tovarying conditions imposed on the device to further reduce the hydraulicand electrical resistance of the ion-exchange device.

In some embodiments, an ion exchange membrane includes a plurality of 3Dprinted spacers adhered to a surface of the ion exchange membrane,wherein the plurality of 3D printed spacers have the followingproperties: a first width W₁ at a first distance L₁ from the membranesurface, a second width W₂ at a second distance L₂ from the membranesurface, W₁>W₂, and L₁>L₂. In some embodiments, the plurality of 3Dprinted spacers have the following additional properties: a third widthW₃ at a third distance L₃ from the membrane surface, W₃>W₂, and L₃<L₂.In some embodiments, the plurality of 3D printed spacers have a heightof 10-1000 microns. In some embodiments, the plurality of 3D printedspacers have a height of 10-250 microns. In some embodiments, an area ofthe surface of the ion exchange membrane covered by the plurality of 3Dprinted spacers is 1-20% of total surface area of the surface of the ionexchange membrane. In some embodiments, a volume of the plurality of 3Dprinted spacers is less than a theoretical maximum volume of theplurality of 3D spacers defined by multiplying a maximum width of thespacers in a x direction by a maximum height of the spacers in a ydirection and by a maximum depth of the spacers in a z direction. Insome embodiments, the volume of the plurality of 3D printed spacers isless than 95% of the theoretical maximum volume of the plurality of 3Dspacers. In some embodiments, a second plurality of 3D printed spacerson a surface of the ion exchange membrane opposite the surface with thefirst plurality of 3D printed spacers. In some embodiments, the ionexchange membrane is a cation exchange membrane or an anion exchangemembrane. In some embodiments, the plurality of 3D printed spacers havethe following additional properties: a first depth D₁ at a firstdistance LD₁ from the membrane surface, a second depth D₂ at a seconddistance LD₂ from the membrane surface, D₁>D₂, and LD₁>LD₂.

In some embodiments, a method of forming an ion exchange membraneincludes 3D printing a plurality of curable spacers on a surface of theion exchange membrane; and curing the plurality of curable 3D printedspacers to form a plurality of 3D printed spacers on the surface of theion exchange membrane, wherein the plurality of 3D printed spacers havethe following properties: a first width W₁ at a first distance L₁ fromthe membrane surface, a second width W₂ at a second distance L₂ from themembrane surface, W₁>W₂, and L₁>L₂. In some embodiments, the pluralityof curable 3D printed spacers is cured by electromagnetic radiation orthermal exposure. In some embodiments, the electromagnetic radiation isultraviolet light. In some embodiments, the plurality of 3D printedspacers have the following additional properties: a third width W₃ at athird distance L₃ from the membrane surface, W₃>W₂, and L₃<L₂. In someembodiments, the plurality of 3D printed spacers have a height of10-1000 microns. In some embodiments, the plurality of 3D printedspacers have a height of 10-250 microns. In some embodiments, an area ofthe surface of the ion exchange membrane covered by the plurality of 3Dprinted spacers is 1-20% of total surface area of the surface of the ionexchange membrane. In some embodiments, a volume of the plurality of 3Dprinted spacers is less than a theoretical maximum volume of theplurality of 3D spacers defined by multiplying a maximum width of thespacers in a x direction by a maximum height of the spacers in a ydirection and by a maximum depth of the spacers in a z direction. Insome embodiments, the volume of the plurality of 3D printed spacers isless than 95% of the theoretical maximum volume of the plurality of 3Dspacers. In some embodiments, the method includes 3D printing a secondplurality of curable spacers on a surface of the ion exchange membraneopposite the surface with the first plurality of 3D printed spacers andcuring the second plurality of curable 3D printed spacers to form asecond plurality of 3D printed spacers on the surface of the ionexchange membrane opposite the surface with the first plurality of 3Dprinted spacers. In some embodiments, the ion exchange membrane is acation exchange membrane or an anion exchange membrane.

In some embodiments, an ion-exchange device includes a pair ofelectrodes comprising an anode and a cathode; a first ion exchangemembrane and a second ion exchange membrane between the pair ofelectrodes, wherein at least one of the first or second ion exchangemembranes includes a plurality of 3D printed spacers adhered to asurface of the at least one of the first or second ion exchangemembranes such that an intermembrane spacing between surfaces of thefirst and second ion exchange membranes is 10-1000 microns, and whereinthe plurality of 3D printed spacers have the following properties: afirst width W₁ at a first distance L₁ from the membrane surface, asecond width W₂ at a second distance L₂ from the membrane surface,W₁>W₂, and L₁>L₂. In some embodiments, the first ion exchange membraneis a cation exchange membrane and the second ion exchange membrane is ananion exchange membrane. In some embodiments, the plurality of 3Dprinted spacers comprise a third width at a third distance from thesurface of the at least one of the first or second ion exchangemembranes, wherein the third width is greater than the second width andthe third distance is less than the second distance. In someembodiments, an area of the surface of the at least one of the first orsecond ion exchange membranes covered by the plurality of 3D printedspacers is 1-20% of total surface area of the surface of the at leastone of the first or second ion exchange membranes. In some embodiments,the plurality of 3D printed spacers have the following additionalproperties: a first depth D₁ at a first distance LD₁ from the membranesurface, a second depth D₂ at a second distance LD₂ from the membranesurface, D₁>D₂, and LD₁>LD₂.

Additional advantages will be readily apparent to those skilled in theart from the following detailed description. The examples anddescriptions herein are to be regarded as illustrative in nature and notrestrictive.

All publications, including patent documents, scientific articles anddatabases, referred to in this application are incorporated by referencein their entirety for all purposes to the same extent as if eachindividual publication were individually incorporated by reference. If adefinition set forth herein is contrary to or otherwise inconsistentwith a definition set forth in the patents, applications, publishedapplications and other publications that are herein incorporated byreference, the definition set forth herein prevails over the definitionthat is incorporated herein by reference.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments are described with reference to the accompanyingfigures, in which:

FIG. 1 illustrates an example of a schematic side view of anion-exchange system disclosed herein.

FIG. 2 illustrates an example of an exploded view of the flow channelsthrough an ion-exchange system disclosed herein.

FIG. 3 illustrates an example of a top view of an ion exchange membranewith adhered spacers.

FIG. 4 illustrates an example of a top view of a close up of the spacersadhered to the ion exchange membrane.

FIG. 5 illustrates an example of an isometric view showing how a spacerborder fits together with an ion exchange membrane.

FIG. 6A illustrates an example of a side view of a 3D printed spacerdisclosed herein.

FIG. 6B illustrates an example of a side view of a 3D printed spacerdisclosed herein.

FIG. 6C illustrates an example of a side view of a 3D printed spacerdisclosed herein.

FIG. 6D illustrates an example of a side view of a 3D printed spacerdisclosed herein.

FIG. 7A illustrates an example of a side view of a 3D printedspring-like spacer disclosed herein.

FIG. 7B illustrates an example of a side view of a 3D printedspring-like spacer disclosed herein.

FIG. 7C illustrates an example of a side view of a 3D printedspring-like spacer disclosed herein.

FIG. 7D illustrates an example of a side view of a 3D printedspring-like spacer disclosed herein.

FIG. 8A illustrates an example of a cross-sectional view of membranesutilizing spring-like spacers with equal flow pressure.

FIG. 8B illustrates an example of a cross-sectional view of membranesutilizing spring-like spacers to vary the thickness of the flow chamberthrough the application of pressure.

FIG. 9 illustrates an example of a flow diagram for making anion-exchange device.

DETAILED DESCRIPTION OF THE DISCLOSURE

The ion-exchange systems and devices disclosed herein include compositeion-exchange membranes that have 3D printed spacers on them. These 3Dprinted spacers can drastically reduce the total intermembrane spacingwithin the system/device while maintaining a reliable sealing surfacearound the exterior border of the membrane. By adding the spacersdirectly to the membrane using additive manufacturing, the amount ofmaterial used can be reduced without adversely impacting themanufacturability of the composite membrane.

In addition, additive manufacturing techniques can allow for thecreation of shapes, features, and patterns of spacers that otherprocesses and conventional spacers do not readily allow. These shapes,features, and patterns can be engineered to improve hydrodynamics andrespond to varying conditions imposed on the device to further reducethe hydraulic and electrical resistance of the ion-exchange device.

The ion-exchange systems and devices disclosed herein can include atleast one pair of electrodes and at least one pair of ion exchangemembranes placed there between. The at least one pair of ion exchangemembranes can include a cation exchange membrane and an anion exchangemembrane. In addition, at least one of the cation exchange membrane andanion exchange membranes has spacers on the surface facing the otherexchange membrane in the ion exchange system/device. In someembodiments, both the cation exchange membranes and the anion exchangemembranes have spacers on at least one surface facing the other exchangemembrane.

FIG. 1 illustrates an example of a schematic side view of anion-exchange system disclosed herein. As shown in FIG. 1 , cationexchange membranes (“CEMs”) and anion exchange membranes (“AEMs”) caninclude spacers (also referred to as posts) on at least one surface ofthe ion exchange membrane. FIG. 3 illustrates an example of a top viewof an ion exchange membrane with adhered spacers to a surface of the ionexchange membrane. In addition, FIG. 4 illustrates an example of a topview of a close up of spacers adhered to the ion exchange membrane. Insome embodiments, the exchange membranes can have spacers on bothsurfaces of the exchange membrane. In addition, the ion-exchange systemsdisclosed herein can have spacers between two adjacent membranes (i.e.,between an anion exchange membrane and a cation exchange membrane). Assuch, the spacers are used to separate the exchange membranes as shownin FIG. 1 .

The system shown in FIG. 1 also includes two electrodes on opposite endsof the device. One electrode can be a cathode and the other electrodecan be an anode. These electrodes can encompass a series of fluidchannels. These fluid channels can be separated by the ion exchangemembranes (e.g., cation exchange membrane and anion exchange membrane).At least some of these fluid channels can receive an influent stream.The influent stream can be water to be purified and can be flowedthrough the channels in between the alternating anionic and cationicexchange membranes. Anion exchange membranes can preferentially allowpassage of negatively charged ions and can substantially block thepassage of positively charged ions. In contrast, cation exchangemembranes can preferentially allow the passage of positively chargedions and can substantially block the passage of negatively charged ions.

The electrolyte fluid channels and streams can be in direct contact withthe electrodes. In addition, these electrolyte streams may include thesame or different fluid as the fluid entering the influent. For example,the electrolyte streams can be a variety of conductive fluids including,but not limited to, raw influent, a separately managed electrolytefluid, NaCl solution, sodium sulfate solution, or iron chloridesolution.

In an ion exchange system such as the one shown in FIG. 1 , when anelectric charge is applied to the electrodes, the ions in the influentstream flowing in the channels between the ion exchange membranes canmigrate towards the electrode of opposite charge. The alternatingarrangement of the ion exchange membranes can thus produce alternatingchannels of decreasing ionic concentration and increasing concentration.The number of channels between the ion exchange membranes may beincreased through the addition of more alternating pairs of membranes toincrease the capacity of the ion exchange system/device. In addition,the functioning ability of an individual ion exchange cell can begreatly augmented by configuring ion exchange cells into ion exchangestacks (i.e., a series of multiple ion exchange cells.)

The influent stream can be converted into a brine stream which istypically waste and a product/diluate stream. The product stream canhave a lower ionic concentration. In some embodiments, the productstream can have a predetermined treatment level. For example, the ionexchange system can remove many types of ions or it could focus or beselective to a specific ion type. Examples of groups of ions caninclude, but are not limited to, monovalent and divalent.

To create the fluid channels between the membranes, spacer borders canbe inserted between the membranes. FIG. 2 illustrates an exploded viewof three membranes and two spacer borders as well as the fluid flow paththrough these components. Specifically, the fluid flow path is shown tobe sequentially cation exchange membrane, spacer border, anion exchangemembrane, spacer border, and cation exchange membrane. In actual use,these components can be sandwiched together such that the spacer bordercan seal against the membranes and provide contained flowchannels/pathways for the fluid to be treated. For example, FIG. 5illustrates an example of an isometric view showing how a spacer borderfits together with an ion exchange membrane. When these components aresandwiched together, the holes in the corners of the various componentsshown in FIG. 2 can create inlet and outlet manifolds. In addition, the3D printed spacers on the ion exchange membranes can provide torturouspaths for the fluid to flow that can increase the turbulence of thefluid flow, but minimize unnecessary pressure drop. The pressure dropcan be minimized compared to conventional woven mesh or extruded nettingspacers by eliminating the cross members that connect the nodes of theseparts. As the 3D printed spacers are connected directly to the membrane,there can be no need for interconnecting parts Eliminating this featurecan present less obstruction in the flow path and may subsequentlyreduce the pressure drop. The manifold holes and the geometry of theadhered spacers can allow the water to flow into and through thecontained area created by the spacer border. In some embodiments, theouter sealing surface outside of the active area of the ion-exchangemembrane can also be 3D printed directly on the membrane. As such, threeindividual components (the ion exchange membrane, the spacers, and thespacer border) can effectively be combined into a single compositemembrane, thereby significantly reducing the complexity of stackingmembranes into a device.

As stated above, FIG. 4 illustrates a close up view of an ion exchangemembrane with adhered spacers. In some embodiments, the spacers can benon-conductive spacers, conductive spacers, or have special ionseparation properties. The spacers shown in FIG. 4 are rectangular(i.e., rectangular blocks) and evenly patterned through the surface ofthe membrane. However, the geometry of the spacers can be different suchas circles (i.e., cylinders), diamonds, or combinations of numerousshapes. Furthermore, the pattern can alternatively be spaced furtherapart or closer together depending on the fluid treatmentspecifications. In addition, the pattern and/or geometry (i.e., 3dimensional shape) of the spacers can be modified throughout the flowpath to provide the greatest turbulence with the minimum pressure drop.This can be quantified using limiting current density with similar 3Dprinted patterns (one intended to create greater mixing than the other).Limiting current density can increase with greater induced turbulence byshrinking the diffusion boundary layer.

By adding the spacers directly to the ion exchange membranes, the totalamount of material used for the spacers can be reduced. This cansubstantially reduce the shadowing effect compared to when usingtraditional spacers. The shadowing effect is a result of anon-conductive spacer blocking (i.e., shadowing) the natural flow ofions resulting from the imposed electric field. In addition, reducingthe amount of spacer material can reduce the amount of flow obstruction.In turn, this can allow for a narrower intermembrane spacing for asimilar applied pressure. Smaller intermembrane spacing can be desirablebecause the amount of voltage required to drive the ion separation isdirectly correlated to the resistance of the water to be treated. Giventhat resistivity is dependent upon path length, the smaller theintermembrane spacing, the lower the total resistance. In someembodiments, the spacers are such that the spacing between ion exchangemembranes can be about 10-1000 microns, about 10-250 microns, or about75-250 microns. In some embodiments, the spacers are such that thespacing between ion exchange membranes can be less than about 1000microns, about 500 microns, about 250 microns, about 100 microns, about50 microns, about 25 microns, about 15 microns, or about 10 microns.

In summation, there can be two primary drivers of energy consumption foran electrochemical ion exchange device: (1) the electrical energyrequired to drive the ion separation; and (2) the hydraulic energyrequired to move the water through the device. Thus, 3D printing spacerson the ion exchange membranes can greatly reduce the intermembranespacing and thus the electrical energy consumed while also reducing theamount of hydraulic energy consumed in the flow field by reducing theamount of spacer material from the spacer.

The spacer itself can be made from a curable polymer solution which canbe applied to an ion exchange membrane by Additive Manufacturing (i.e.,3D Printing) in a desired shape and pattern. 3D printing can allow for asimplified manufacturing process over traditional spacer manufacturingprocesses such as screen-printing. For example, 3D printing caneliminate excess material used for the spacers or molds required toimpart a desired shape. Additionally, by eliminating the need for amold, 3D printing can remove various cleaning steps and/orwaste/maintenance associated with damage to the molds.

Another important benefit of 3D printing is that it can allow for themanufacture of more complex shapes and patterns which cannot be producedvia previously described spacer formation methods such asscreen-printing. For example, FIGS. 6A-D illustrate examples of a sideview of 3D printed spacers disclosed herein. As shown in FIGS. 6A-D, thespacers have reduced material (i.e., less volume) compared totraditional spacers. The spacers can have a maximum width in the xdirection (i.e., x axis), a maximum height in the y direction (i.e., yaxis), and a maximum depth in the z direction (i.e., z axis). In someembodiments, the 3D printed spacers can have volume that is less than atheoretical maximum volume defined by the maximum width multiplied bythe maximum height multiplied by the maximum depth (i.e., MaxTheoretical Volume=max width×max height×max depth). In some embodiments,the volume of the spacer can be less than about 95%, about 90%, about85%, about 80%, about 75%, about 70%, about 65%, about 60%, about 55%,about 50%, about 45%, or about 40% of the theoretical maximum volume ofthe spacer.

In some embodiments, the height of the spacers can be about 10-1000microns, about 10-250 microns, or about 75-250 microns. In someembodiments, the height of the spacers can be less than about 1000microns, about 500 microns, about 250 microns, about 100 microns, about50 microns, about 25 microns, about 15 microns, or about 10 microns. Insome embodiments, the width of the spacers can be less than or equal toabout 100 microns, about 90 microns, about 80 microns, about 70 microns,about 60 microns, about 50 microns, or about 40 microns. In someembodiments, the depth of the spacers can be less than or equal to about100 microns, about 90 microns, about 80 microns, about 70 microns, about60 microns, about 50 microns, or about 40 microns.

In some embodiments, the width in the x direction of the spacer can varydepending on the distance from the membrane in the y direction. Forexample, the 3D printed spacer can have at least a first width at afirst distance from the membrane and a second width at a second distancefrom the membrane. There can be many more different widths of the spacerat many more distances from the membrane. In some embodiments, the firstwidth of the spacer can be greater than the second width of the spacer.In some embodiments, the first distance from the membrane can be greaterthan the second distance from the membrane. In some embodiments, the 3Dprinted spacer can have a third width at a third distance from themembrane, wherein the third width of the spacer can be greater than thesecond width of the spacer and the third distance from the membrane canbe less than the second distance from the membrane.

For example, FIG. 6C represents an hourglass type geometry that has awidth W1 at a distance L1 from the membrane, a width W2 at a distance L2from the membrane, and a width W3 at a distance L3 from the membrane. Asshown in FIG. 6C, width W1 is greater than width W2 and distance L1 isgreater than distance L2. In addition, width W3 is greater than width W2and distance L2 is greater than distance L3. Such geometry of the spaceris incapable of being formed by traditional screen-printing methods.

In some embodiments, the depth in the z direction of the spacer can varydepending on the distance from the membrane in the y direction. Forexample, the 3D printed spacer can have at least a first depth at afirst distance from the membrane and a second depth at a second distancefrom the membrane. There can be many more different depths of the spacerat many more distances from the membrane. In some embodiments, the firstdepth of the spacer can be greater than the second depth of the spacer.In some embodiments, the first distance from the membrane can be greaterthan the second distance from the membrane. In some embodiments, the 3Dprinted spacer can have a third depth at a third distance from themembrane, wherein the third depth of the spacer can be greater than thesecond depth of the spacer and the third distance from the membrane canbe less than the second distance from the membrane.

In some embodiments, the cross sectional area of a single 3D printedspacer taken through the width of the spacer can vary depending on thedistance from the membrane in the y direction. For example, the 3Dprinted spacer can have at least a first cross sectional area at a firstdistance from the membrane and a second cross sectional area at a seconddistance from the membrane. There can be many more cross sectional areasof the spacer at many more distances from the membrane. In someembodiments, the first cross sectional area of the spacer can be greaterthan the second cross sectional area of the spacer. In some embodiments,the first distance from the membrane can be greater than the seconddistance from the membrane. Furthermore, proper adhesion to the membranecan be maintained by increasing the area where the spacer contacts themembrane while maintaining a minimum thickness in the center section ofthe spacer to minimize obstruction to flow. As such, in someembodiments, the 3D printed spacer can have a third cross sectional areaat a third distance from the membrane, wherein the third cross sectionalarea of the spacer can be greater than the second cross sectional areaof the spacer and the third distance from the membrane can be less thanthe second distance from the membrane.

In addition, the complex shapes that are capable of being printed usingAdditive Manufacturing can allow for decreased flow obstruction withoutcompromising the desired membrane separation. An additional benefit to3D printing the spacers is that the total height of the printed spacerscan be varied along the width and length of the membrane.

The spacers can also be combined with operational decisions to improvethe performance of the ion-exchange systems. For example, the spacerscan be designed such that they have the ability to compress and/orexpand (i.e., spring-like) under the application/removal of a load. Inthis way, the spacers can act like a spring having a spring constantthat can be used to alter the height/thickness of the fluid flowchannels by manipulating the relative pressures of the product/diluateand brine streams. As such, the thickness of the product/diluate streamcan be reduced by increasing the pressure of the brine stream relativeto the product/diluate stream, which in turn can reduce the resistanceof the product/diluate stream. Examples of spring-like spacers can beshown in FIG. 7A-D.

The spring-like spacers can expand or contract to fill the intermembranegap. In some embodiments, the spacer can contact both membranes at alltimes to ensure proper flow distribution. In some embodiments, thespring constant of the spacers can vary such that the width of thechannels can be graded throughout the length of the flow channels. Insome embodiments, the spacers can have a spring constant of about 5-2000N/m or about 20-200 N/m. In addition, the height of the spring-likespacer may be greater than the desired intermembrane gap to allow forproper expansion as pressure is applied to either the product/diluate orbrine stream. For example, in some embodiments, the flows can beconfigured to be in a co-flow arrangement as shown in FIG. 8A-B. In theco-flow arrangement, the direction of the brine stream runs in the samedirection as the product/diluate stream.

In some embodiments, equal pressure can be applied to both chambers(i.e., pressure from the brine stream=pressure from the product/diluatestream) such that the spring-like spacers allow for equal intermembranespacing. However, in some embodiments, the brine stream can bepressurized as shown in FIG. 8B such that the beneficial differentialpressure can be maintained throughout the length of the flow channels.This additional pressure can increase the intermembrane spacing in thebrine flow channel as the spring-like spacers expand. Conversely, theintermembrane spacing in the product/diluate flow channel can decreaseas the spring-like spacers in that channel compress. This reduction inthickness can reduce the electrical resistance attributed to theproduct/diluate flow channel and the electrodialysis stack.

In some embodiments, the flows of the streams can be configured in“counter flow” where the direction of the brine stream is opposite thedirection of the product/diluate stream. In this configuration, thepressure drop across the length of the flow channel can be utilized toconstrict the width of the product/diluate stream at the exit. This candeliver the benefit where it is most needed because the conductivity isreduced over the length of the flow channel as ions are removed from theproduct stream in the ion-exchange process.

In some embodiments, the spacers can be designed to allow for a greaterintermembrane spacing at the inlets and/or outlets of the contained areacreated by the spacer border. The pressure drop associated withintroducing fluid through this portion of the cell can be a significantfraction of the total pressure drop. By increasing the thickness of thespacer in the inlet, the associated pressure drop of the inlet to theactive area can be reduced. In addition, as discussed above, the spacerscan be such that it expands and/or contracts to produce the desiredthickness in the active area of the flow chambers while maintaining amore open flow in the inlet region.

A flow diagram for making an ion-exchange device is shown in FIG. 9 .After a surface of an ion exchange membrane is cleaned and exposed, acurable polymer material/solution can be applied to the exposed ionexchange membrane's surface. The desired geometry and pattern of thespacers can be created in a drawing software application and saved as amethod file. The membrane can then be loaded into the 3D printer andaligned such that the printer head can apply the curable spacer materialto the desired locations. Upon completion of the method file, the spacermaterial can be cured such that it will adhere to the ion exchangemembrane surface. In some embodiments, the spacer material can be curedby irradiation with electromagnetic radiation (e.g., ultraviolet lightor an electron beam) or thermal exposure. The source of radiation orheat may be any source which can provide the wavelength and/or intensityof radiation or heat necessary to cure the spacer composition.

In some embodiments, the extent to which the ion exchange membranesurface is covered by spacers (i.e., the Spacer %) may be expressed bythe following equation: Spacer %=(Area of Spacers/Active MembraneArea)*100%. Area of Spacers is the area of the membrane which extendsoutward from the plan of the membrane on the relevant side, measuredwhere the spacers meet the plane of the membrane (e.g., the base area ofthe spacers). Active Membrane Area is the total active area the relevantside of the membrane would have if it were without spacers and nottextured, wherein active means the area that comes into contact withliquid when the membrane is in use (i.e., excluding the area of themembrane which forms the seal). In some embodiments, the Spacer % can beabout 1-20%, about 2-15%, about 3-13%, about 4-11%, about 5-10%, about7-9%, or about 8%. In some embodiments, the Spacer % can be about 8-13%.

This process can be repeated for all the desired ion exchange membranes(cation and anion exchange membranes) as well as additional surfaces ofthe desired ion exchange membranes in the ion exchange device. Afterprinting the ion exchange membranes can be sized for incorporation intothe device. The ion exchange membranes can next be arranged into an ionexchange device by alternating cation and anion exchange membranes. Insome embodiments, a spacer border (with inlets to control the directionof flow) can be placed in between the cation and anion exchangemembranes. In other embodiments, the spacer border can also be printedon the ion exchange membrane, thereby further reducing the number ofcomponents in the assembly and reducing complexity of the stackingprocedure.

EXAMPLE

In one example, a curable polymeric material is first loaded into a 3Dprinter. The desired printed pattern is then programmed into a methodfile, which is then used to deposit the polymeric material in thedesired size and shape onto the membrane surface. In one exemplary case,the rectangle spacers and inter-spacer spacing is chosen to a Spacer %of 13%. This process can have the advantage of not needing a mold toform the spacers, can reduce waste of the curable polymer material, andcan remove cleaning steps that accompany the use/re-use of a mold.

Definitions

Unless defined otherwise, all terms of art, notations and othertechnical and scientific terms or terminology used herein are intendedto have the same meaning as is commonly understood by one of ordinaryskill in the art to which the claimed subject matter pertains. In somecases, terms with commonly understood meanings are defined herein forclarity and/or for ready reference, and the inclusion of suchdefinitions herein should not necessarily be construed to represent asubstantial difference over what is generally understood in the art.

Reference to “about” a value or parameter herein includes (anddescribes) variations that are directed to that value or parameter perse. For example, description referring to “about X” includes descriptionof “X”. In addition, reference to phrases “less than”, “greater than”,“at most”, “at least”, “less than or equal to”, “greater than or equalto”, or other similar phrases followed by a string of values orparameters is meant to apply the phrase to each value or parameter inthe string of values or parameters. For example, the spacing between ionexchange membranes can be less than about 1000 microns, about 500microns, or about 250 microns is meant to mean that the spacing betweenion exchange membranes can be less than about 1000 microns, less thanabout 500 microns, or less than about 250 microns.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It is also to be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It is further to beunderstood that the terms “includes, “including,” “comprises,” and/or“comprising,” when used herein, specify the presence of stated features,integers, steps, operations, elements, components, and/or units but donot preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, units, and/or groupsthereof.

This application discloses several numerical ranges in the text andfigures. The numerical ranges disclosed inherently support any range orvalue within the disclosed numerical ranges, including the endpoints,even though a precise range limitation is not stated verbatim in thespecification because this disclosure can be practiced throughout thedisclosed numerical ranges.

The above description is presented to enable a person skilled in the artto make and use the disclosure, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the disclosure. Thus, this disclosure is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

1. A method of forming an ion exchange membrane, comprising: 3D printinga plurality of curable spacers on a surface of the ion exchangemembrane; and curing the plurality of curable 3D printed spacers to forma plurality of 3D printed spacers on the surface of the ion exchangemembrane, wherein the plurality of 3D printed spacers have the followingproperties: a first width W₁ at a first distance L₁ from the membranesurface, a second width W₂ at a second distance L₂ from the membranesurface, W₁>W₂, and L₁>L₂.
 2. The method of claim 1, wherein theplurality of curable 3D printed spacers is cured by electromagneticradiation or thermal exposure.
 3. The method of claim 2, wherein theelectromagnetic radiation is ultraviolet light.
 4. The method of claim1, wherein the plurality of 3D printed spacers have the followingadditional properties: a third width W₃ at a third distance L₃ from themembrane surface, W₃>W₂, and L₃<L₂.
 5. The method of claim 1, whereinthe plurality of 3D printed spacers have a height of 10-1000 microns. 6.The method of claim 5, wherein the plurality of 3D printed spacers havea height of 10-250 microns.
 7. The method of claim 1, wherein an area ofthe surface of the ion exchange membrane covered by the plurality of 3Dprinted spacers is 1-20% of total surface area of the surface of the ionexchange membrane.
 8. The method of claim 1, wherein a volume of theplurality of 3D printed spacers is less than a theoretical maximumvolume of the plurality of 3D spacers defined by multiplying a maximumwidth of the spacers in a x direction by a maximum height of the spacersin a y direction and by a maximum depth of the spacers in a z direction.9. The method of claim 8, wherein the volume of the plurality of 3Dprinted spacers is less than 95% of the theoretical maximum volume ofthe plurality of 3D spacers.
 10. The method of claim 1, furthercomprising 3D printing a second plurality of curable spacers on asurface of the ion exchange membrane opposite the surface with the firstplurality of 3D printed spacers and curing the second plurality ofcurable 3D printed spacers to form a second plurality of 3D printedspacers on the surface of the ion exchange membrane opposite the surfacewith the first plurality of 3D printed spacers.
 11. The method of claim1, wherein ion exchange membrane is a cation exchange membrane or ananion exchange membrane.
 12. An ion-exchange device comprising: a pairof electrodes comprising an anode and a cathode; a first ion exchangemembrane and a second ion exchange membrane between the pair ofelectrodes, wherein at least one of the first or second ion exchangemembranes comprises a plurality of 3D printed spacers adhered to asurface of the at least one of the first or second ion exchangemembranes such that an intermembrane spacing between surfaces of thefirst and second ion exchange membranes is 10-1000 microns, and whereinthe plurality of 3D printed spacers have the following properties: afirst width W₁ at a first distance L₁ from the membrane surface, asecond width W₂ at a second distance L₂ from the membrane surface,W₁>W₂, and L₁>L₂.
 13. The device of claim 12, wherein the first ionexchange membrane is a cation exchange membrane and the second ionexchange membrane is an anion exchange membrane.
 14. The device of claim12, wherein the plurality of 3D printed spacers comprise a third widthat a third distance from the surface of the at least one of the first orsecond ion exchange membranes, wherein the third width is greater thanthe second width and the third distance is less than the seconddistance.
 15. The device of claim 12, wherein an area of the surface ofthe at least one of the first or second ion exchange membranes coveredby the plurality of 3D printed spacers is 1-20% of total surface area ofthe surface of the at least one of the first or second ion exchangemembranes.
 16. The device of claim 12, wherein the plurality of 3Dprinted spacers have the following additional properties: a first depthD₁ at a first distance LD₁ from the membrane surface, a second depth D₂at a second distance LD₂ from the membrane surface, D₁>D₂, and LD₁>LD₂.